The present invention generally relates to optical fiber connectors, more particularly, to stackable ferrules for terminating optical fiber ribbons.
Advances in lightwave technology have made optical fiber a very popular medium for large bandwidth applications. In particular, optical technology is being utilized more and more in broadband systems wherein communications between systems take place on high-speed optical channels. As this trend continues to gain more and more momentum, the need for efficient utilization of the precious real estate on circuit boards, racks/shelves, back planes, distribution cabinets, etc., is becoming ever increasingly important. In order to fulfill expectations across the industry, opto-electronic modules and optic fiber devices need to continue to become miniaturized, thereby taking full advantage of the maturity of micro- and opto-electronic technologies for generating, transporting, managing and delivering broadband services to the ever increasing bandwidth demands of end users at increasingly lower costs. Thus, the industry has placed an emphasis on small form factor optical connectors, such as the LC connector from Lucent Technologies, Inc. However, miniaturization is tempered by the requirements of transmission efficiency. For instance, with the advent of new standards such as gigabit ethernet, wherein the transmission efficiency is becoming more and more critical, the performance of optical connectors is becoming correspondingly important for healthy operation of the system. Thus, it is desirable to obtain component miniaturization without sacrificing transmission efficiency, and sometimes while improving transmission efficiency.
With the miniaturization of optical modules and optical fiber devices, the management of optical fiber congestion has become an issue at optical interfaces and connection distribution points. One solution is the use of multi-fiber ribbon in which a plurality of optical fibers are organized and molded side by side in a plastic ribbon. It is known to interconnect these ribbon cables by supporting the fibers between two support members made of a monocrystalline material, such as silicon. In the support members are V-grooves formed utilizing photolithographic masking and etching techniques. The fibers are placed side by side in individual V-grooves of one support member and the other mating support member having corresponding V-grooves is placed over the fibers so as to bind or hold the fibers in a high precision, spatial relationship between the mating V-grooves. The top and bottom support members sandwiching the multi-fiber ribbon are typically bonded together with a clamp or adhesive, forming a ferrule of a multi-fiber connector. Two mating ferrules with the same fiber spacing may then be placed in an abutting relationship so that the ends of the fibers of the respective ferrules are substantially co-axially aligned with one another, thereby forming a multi-fiber connection. If desired, such ferrules can be stacked in order to increase the interconnection density.
Multi-fiber ribbons and connectors have numerous applications in optic communication systems. For instance, some opto-electronic and optical application specific integrated circuits (OASIC) devices, e.g., optical switches, optical power splitters/combiners, routers, etc., have several input and/or output ports arranged as linear arrays to which a plurality of fiber are to be coupled. Further, since optical fibers are attached somehow to launch optical signals into these devices and extract optical signals out of these devices, splicing of arrays of fibers (i.e., a multi-fiber ribbon) to such devices can be achieved using muti-fiber connectors. Yet another possible application relates to an optical fan-out fabric where an array of fibers in a multi-fiber ribbon may be broken into simplex or duplex channels for distribution purposes, as is often desired.
A critical factor to the optical efficiency of a multi-fiber ferrule, whether or not stacked, is the alignment of the mating ferrules with regard to one another. To that end, alignment pins are often utilized. Alignment pins are received in alignment pin holes or slots in the respective ferrules so as to hold the ferrules in precise alignment with regard to one another. The alignment pins usually extend parallel to the optical fibers, and are preferably made of a material have a similar coefficient of thermal expansion to the ferrules. In one embodiment, as disclosed in U.S. Pat. No. 4,973,127 to Cannon Jr. et al., alignment pin holes are formed by grooves that are laterally disposed on opposite sides of the optical fiber V-grooves in the support members, such that when two support members are brought together, alignment pin holes are defined by mating alignment grooves. In U.S. Pat. No. 5,620,634 to the present inventor, wherein support members are stacked in order to increase the interconnection density, alignment slots are provided on each row of optical fiber, that is, every support member interface.
In summary, there continues to exist a need to further miniaturize optical fiber connections and, at the same time, to increase inner connection density while conforming to interface standards.
The present invention is a stackable multi-fiber ferrule that enables relatively tighter stacking between fiber arrays, resulting in increased interconnection density. The present invention achieves tighter stacking by incorporating an inner support member having alignment pin grooves on only one side. Thus, the thickness of the inner support member may be thinner than that of conventional support members because the inner support member of the present invention does not have to accommodate opposing alignment pin grooves on both sides thereof.
Thus, a multi-fiber stackable ferrule in accordance with the present invention will not have alignment pin holes for every row of fibers but will, instead, have alignment pin holes only on alternating rows of fibers, that is, on every other interface between adjacent support members. However, there is a minimum of two alignment pin holes per stackable ferrule, which is considered the minimum number to maintain alignment and prevent rotation movement of a stackable ferrule with respect to a mating ferrule or device. Accordingly, a stackable multi-fiber ferrule in accordance with the present invention is capable of establishing a highly efficient optical connection.
In accordance with an aspect of the present invention, a stackable multi-fiber ferrule comprises first and second outer support members and at least one inner support member positioned between the outer support members. Each of the outer support members includes a first array of parallel grooves and at least a first alignment pin groove formed in a first surface thereof. In addition, each inner support member includes a second array of parallel grooves formed in a first surface thereof and a third array of parallel grooves formed in a second surface thereof. Each inner support member also includes a second alignment pin groove and a third alignment pin groove. The inner support member is interposed between the first and second outer support members forming at least one interface, and wherein one of the first alignment pin grooves of one of the first and second outer support members and one of the second and third alignment pin grooves of the inner support member form an alignment pin hole at the first interface. The second alignment pin groove may be formed in the first surface and the third alignment pin groove may be formed in the second surface of the inner support member. Alternatively, the second alignment pin groove and the third alignment pin groove may be both formed in the first surface of the inner support member.
The stackable multi-fiber ferrule may further include a second inner support member interposed between the inner support member and one of the first and second outer support members forming a second interface between the second inner support member and the one of the first and second outer support members. The second inner support member may further form a third interface between the inner support member and the second inner support member. The second inner support member may further includes fourth and fifth alignment pin grooves wherein one of the first alignment pin grooves of one of the first and second outer support members and one of the fourth and fifth alignment pin grooves form a second alignment pin hole at the second interface.
The stackable multi-fiber ferrule may further include a plurality of substantially identical inner support members interposed between the first and second outer members, wherein alignment pin holes are defined not at every interface, but at alternating interfaces. Further, the inner support member has a thickness and the second alignment pin groove has a depth, wherein the depth is sufficient with respect to the thickness to prevent the alignment pin grooves from being formed opposite one another.
In accordance with another aspect of the present invention, a stackable multi-fiber ferrule system terminating at least first and second optical fiber ribbons comprises an inner support member including a first array of parallel grooves formed in a first surface thereof and a second array of parallel grooves formed in a second surface thereof. The ferrule system further includes substantially identical first and second outer support members sandwiching the inner support member, wherein each of the first and second outer members includes a third array of parallel grooves formed in a first surface thereof.
The first optical fiber ribbon terminates and is held at a first interface between the first array of parallel grooves and the third array of parallel grooves of the first outer support member. However, the second optical fiber ribbon can be held between the second array of parallel grooves and the third array of parallel grooves of the second outer support member. Further, the inner support member and the first outer support member can include mating alignment pin grooves that form first and second alignment pin holes at the first interface.
The first optic fiber ribbon can include a first end that terminates at the stackable multi-fiber ferrule and a second end that terminates at a second stackable multi-fiber ferrule. The first optical fiber ribbon can also include a plurality of individual optical fibers having respective ends, wherein a first portion of the plurality of optical fibers are terminated at respective ends by a second stackable multi-fiber ferrule and a second portion of the plurality of said optical fibers are terminated at respective ends by a third stackable multi-fiber ferrule.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such features and advantages be included herein within the scope of the present invention as defined by the appended claims.